Silt and soil erosion control methods are employed to prevent soil and sand run-off from a land site caused by water, such as that resulting from heavy rainfall. These control methods are particularly important to the building and road construction industry, and generally involve use of some form of a barrier around the site to impede silt, soil and sand run-off while permitting water drainage from the site.
The barrier used in these control methods sometimes is in the form of a fence, such as disclosed in U.S. Pat. No. 4,671,495, where the fence is built from slats that are attached to posts and rotate partially around the posts, or in U.S. Pat. No. 3,426,536, where the fence is built from pliable strips and posts, with the strips alternately plaited through the posts perpendicular to the ground.
Fences have also been used for snow control purposes. U.S. Pat. No. 514,999 describes a metal snow fence of broad metal bands interwoven with a metal thread. U.S. Pat. No. 3,672,638 describes a snow fence made from a wire fabric containing warp and weft wires. The warp wires each have a diameter of between 0.011 and 0.018 inches, and are finer than the weft wires. The weft wires extend perpendicular to the warp wires, having a diameter of between 0.018 and 0.047 inches and a weft density of 4 to 8 wires per inch. The fence fabric also has a plurality of slat portions in the warp direction that alternates with open portions. Within the slat portions, the warp density is between 15 and 40 wires per inch, being greater at the upper and lower edge to provide selvage effects. In addition, to bind the wires, the fabric has a coating which encases the warp and weft wires but does not close the interstices within the slat portions.
Woven silt control fabrics using synthetic yarns have been used increasingly in recent years to prevent soil run-off from construction sites. Woven silt control fabrics are generally designed to have water flow capacity of about 20 or above gallons per minute per square foot of fabric (gal/min/ft.sup.2), while retaining soil particles greater than 20 apparent opening size (AOS), also termed equivalent opening size (EOS). (Apparent opening size numbers correspond to U.S. sieve size; for example, a 20 AOS equals a 20 sieve and a 30 AOS equals a 30 sieve.) For example, two woven silt control fabrics sold by Amoco Fabrics & Fibers Company, and designated as Number 1380 and Number 2125 in a brochure entitled "WOVEN FABRIC SELECTION GUIDE," have water flow capacities, also called permitivities, of 30 and 15 gal/min/ft.sup.2, respectively, while having an AOS of between 20 to 30 and between 30 to 50, respectively. The State of Georgia is a leading user of silt control fabric and the State of Georgia Department of Transportation silt control fence specifications, entitled Specification Section 171-"Temporary Silt Fence," published Nov. 4, 1988, specify a water flow capacity of 25 gal/min/ft.sup.2 and an AOS of 30, and specify use of slit tape yarns in only one direction, either warp or fill.
Woven silt control fabrics have been made using various fabric design methods. First, yarns of substantially flat and rectangular cross-sections, sometimes called tape or ribbon yarns, have been used in silt control fabrics as both the warp and the fill yarns, which are woven together using a plain weave. The aforementioned Amoco Fabric No. 2125 is of this type. These fabrics have been used successfully for silt control, although the size of the openings in the fabric can be inconsistent because of the presence of flip turns (or folds) resulting occasionally from insertion of the weft yarns during the weaving process. Such fabrics thus cannot always retain all soil particles of a certain size, since the maximum opening size, which equals that resulting from the flip turns, may be too large.
A second fabric, available from Belton Industries, employs very wide, flat tape yarns in the warp and weft, which are woven together with a twill-type weave in a highly compacted fashion in each of the warp and weft. This fabric design is limited in that high water flow rates through the fabric concomitant with retention of small soil particles cannot be achieved with it.
Silt control fabrics also have been woven from tape yarns and either bulked continuous filament (BCF) yarns or spun yarns. The aforementioned Amoco Fabric No. 1380 is of this type using spun polypropylene yarns. Each of the BCF and spun yarns are relatively more expensive, making these fabrics significantly more expensive; they thus find use only in specialty applications or in applications with minimal requirements for fabric strength and lifetime, which permit use of second-quality BCF or spun yarns to lower fabric cost.
Various woven fabric constructions and yarn types have been used for applications other than silt control. For example, in the Amoco Fabrics and Fibers Company Brochure discussed previously, Fabric No. 1198, used for "Embankment/Erosion Control," is made with monofilament yarns in the warp and weft. The monofilament yarns in the warp of this fabric are shaped like narrow flat yarns, with a low "aspect ratio", which is used herein means the ratio of yarn width to yarn thickness. This fabric does not employ compaction of the warp yarns.
U.S. Pat. No. 4,590,121 describes a woven sail cloth with spaced fibrous yarns woven in one direction and spaced tapes at least four times wider than the yarns in a perpendicular direction. This sail cloth fabric is disclosed as having greatly reduced porosity and as having the advantage of being made with less loom time.
U.S. Pat. No. 3,317,366 describes a woven polyester fabric for carpet that consists of a warp of flat monofilaments and a fill of multifiber yarns. This backing is said to exhibit improved dimensional stability and avoid needle deflection in the tufting operation.
U.S. Pat. No. 3,252,484 describes a fabric adapted for adhering to a textile fabric when in contact with the textile fabric under application of heat and pressure. This adhesive fabric employs one series of yarns made by doubling thermoplastic yarns with non-thermoplastic yarns which are then woven with another series of non-thermoplastic yarns.
U.S. Pat. No. 3,540,587 describes a method for depositing particles by using a thermoplastic sheet make of strips of thermoplastic filaments, wherein the filaments are used as a reinforcement in at least two directions. This fabric is disclosed as useful for beach erosion control.
U.S. Pat. No. 1,964,419 describes a porous textile fabric designed for filtration, which is made from a wide mesh base fabric. Threads are added in the warp direction which stay on one side of the fabric and are woven with added threads in the fill direction which stay on the opposite side of the fabric.
U.S. Pat. No. 1,659,680 describes a woven tire cord fabric, wherein the warp yarns are designed to lie flat and parallel throughout the warp, consisting of a set of relatively coarse cords as a warp and a relatively fine set of wefts, spaced at a distance equal to several diameters of the warps, which are interwoven by having each weft pass over one warp and then under several warps.
U.S. Pat. No. 904,350 describes a fabric for use in the body portion of bags or luggage consisting of a warp with flat strips and with warp threads lying parallel to the strips and between them, interwoven with weft threads which are either flat or round.
U.S. Pat. No. 3,283,788 describes a process for producing a textile fabric made from thermoplastic materials wherein split fibers lying in one direction are interlaced with threads, filaments or yarns lying in a transverse direction.
U.S. Pat. No. 4,421,439 describes a soil bearing fabric, for use in building on top of bad subsoils, made from a warp having straight warp yarns and binder warp yarns, with each straight warp yarn having a higher strength than the binder warp yarns. The warp contains 2-15 straight yarns and 2-15 binder yarns per centimeter of fabric. The fabric disclosed therein is not compacted in the warp and the straight warp yarns and binder warp yarns are disclosed as being formed by multifilament yarns, monofilament yarns, flat yarn or split fibers.
Great Britain Patent 811,108 describes a flexible material, for use as a belting material, made from a ribbed, reinforcing fabric covered with an elastomer. The reinforcing fabric is made with warp yarns having little crimp alternating with warp yarns having substantial crimp. The two example fabrics in this patent are disclosed as constructed with 24 ends and 15 and 16 picks, respectively. This fabric is not described as compacted in the warp or as using flat yarns.
U.S. Pat. No. 4,362,199, and its related patent Gr. Britain 1,591,091, describe a bulk storage bag made with a woven fabric which is strengthened and reinforced by adding different yarn threads to the fabric. These patents also discuss a technique sometimes referred to as "cramming," which is defined as increasing the number of warps of thread per unit length of that portion of fabric containing the added threads to at least 1.4 times the number of warps per unit length in the other portions of the fabric.
U.S. Pat. No. 4,207,937 describes a storage bag using a crammed fabric to add strength near the selvages in the fabric. Great Britain Patent 2,132,171A describes cramming in the warp of the bulk container fabric. European Patent Application 0212835, filed Jul. 14, 1986, describes cramming of the warp threads to provide reinforcing bands to add strength in such bulk container bags. U.S. Pat. No. 4,390,044 describes an apparatus for producing a fabric having crammed weft threads.
The existing woven silt control fabrics generally are not able to achieve relatively high water flow rates through the fabric while at the same time retaining relatively smaller soil particles. It is an object of this invention to provide an improved silt control fabric. It is another object to provide such a silt control fabric capable of high water flow rates and high soil retention. It is a further object to provide a silt control fabric having a longer life expectancy. It is yet another object to provide an inexpensive silt control fabric.
We have found that the objects of the invention can be achieved by providing a woven silt control fabric in which substantially flat tape yarns and substantially round monofilament yarns are woven in a particular construction to create a fabric substantially lacking in gaps or open spaces having angles of incidence substantially perpendicular to the plane of the fabric surface while having a plurality of substantially triangular shaped gaps having angles of incidence other than substantially perpendicular to the plane of the fabric surface.